The present invention relates to an electric hand that uses an electric motor to perform opening/closing motion of jaw members that performs workpiece-holding operation, and particularly to an electric hand using a stepping motor.
1. Prior Art
As hands for holding various workpieces for processing, transporting, and the like, electric hands that use an electric motor to perform opening/closing motion of jaw members are known. The electric hand performs opening/closing control step-by-step at very small pitches for the jaw members according to the number of driving pulses, thereby allowing the jaw members to perform the opening/closing motion corresponding to the size of an object to be held.
With the stepping motor being used, an arrangement must be made such that the opening width of the jaw members that is set according to the number of the driving pulses agrees with the width of a portion of a workpiece that is held. Alternatively, an arrangement must be made such that the number of the driving pulses is slightly increased to make the holding width of the jaw members to be somewhat smaller than the width of a workpiece. Then, the electric hand must perform the holding motion by allowing workpiece-holding attachments provided on the jaw members to flexibly bend.
However, the sizes of workpieces are not constant. Therefore, the number of the pulses for driving the motor must be adjusted according to the sizes of the workpieces. Practically, however, such adjustment for various workpieces is difficult. Also, either in a case where the object-holding attachments provided on the jaw members do not flex or in a case where the jaw members perform the holding motion beyond the flexing range of the attachments, an out-of-synchronism phenomenon where the driving pulses are not kept in synchronism with the stepping motor occurs, and the electric hand thereby causes an operational defect.
2. Disclosure of the Invention
The present invention has been made to solve the above-described problems. Accordingly, an object of the invention is to provide an electric hand using a stepping motor, in which an operational defect due to out-of-synchronism in pulse is prevented, a holding width of jaw members that corresponds to the width of a workpiece is secured, and the workpiece can therefore be securely held.
To achieve the above, according to the present invention, an electric hand has a buffering mechanism for over-rotating a stepping motor in a buffered manner within a preset range of the number of pulses when a workpiece is held by a pair of jaw members.
The buffering mechanism has a driving-side member that operates together with an output shaft of the stepping motor, a driven-side member that operates together with the pair of jaw members, and spring means interposed between the driving-side member and the driven-side member. The driving-side member is directly engaged with the driven-side member to allow a driving force to be directly transmitted from the output shaft to jaw members when the jaw members are opened. The driving-side member is engaged with the driven-side member via the spring means to allow the driving force to be elastically transmitted from the output shaft to the jaw members via the spring means when the workpiece is held by the jaw members.
In the electric hand configured as described above, even after the jaw members hold the workpiece, the output shaft of the stepping motor can be elastically over-rotated. Therefore, by preliminarily setting the number of driving pulses for the stepping motor within a range permitting the aforementioned over-rotation, the workpiece can be securely held without causing an operational defect due to out-of-synchronism between the stepping motor and the driving pulses.
According to a specific aspect of the present invention, the aforementioned converting mechanism has a rotation shaft that is mounted on the output shaft of the stepping motor, a driving member that is screw-connected with the rotation shaft and that is linearly moved forward and backward along the axial direction according to reciprocating and rotating motion of the rotation shaft, and an opening/closing mechanism for converting linear movement transmitted from the driving member to the opening/closing motion of the pair of jaw members via a transmission shaft. In addition, the spring means is interposed between the driving member and the transmission shaft, so that the buffering mechanism is configured of the driving member, the transmission shaft, and the spring means.
More particularly, the aforementioned driving member has a hollow buffer housing on a distal end side, a proximal end portion of the transmission shaft is received in the buffer housing so as to be slidable by a specific distance, and the aforementioned spring means is interposed between a flange portion formed on the transmission shaft and the buffer housing.
According to another specific aspect of the invention, the aforementioned converting mechanism has a pinion fixed to the output shaft of the stepping motor, a pair of driving members having racks meshing with the pinion, and a pair of transmission members each interposed between each driving member and each jaw member for transmitting motion of each driving member to each jaw member to open/close the pair of jaw members. In this configuration, the aforementioned spring means is interposed between the pair of driving members and the pair of transmission members, so that the aforementioned buffering mechanism is formed of the driving members, the transmission members, and the spring means.
More particularly, the aforementioned transmission members are respectively received in the driving members that are cylindrical so as to be slidable by a specific distance and are connected to the jaw members via driving pins extending from the transmission members, and the spring means is interposed between the transmission members and the driving members so as to elastically urge the transmission members in the direction for holding operation.
According to still another specific aspect of the invention, the aforementioned converting mechanism has a rotation member mounted on the output shaft of the stepping motor; a cam member mounted on the rotation member; a pair of cam grooves that are shaped substantially to be semicircular and that are formed in the cam member; and driving pins that are respectively fixed on the pair of jaw members, that are individually fitted into the pair of cam grooves, and that slide in the cam grooves according to rotation of the cam member to open/close the jaw members. Also, the aforementioned rotation member has a base stand fixed to the output shaft, and a mounting stand assembled to the base portion so as to be rotatable relative to the base stand by a specific angle; the cam member is installed on the mounting stand, the spring means is interposed between the base portion and the mounting stand, and the buffering mechanism is configured of the base portion, the mounting stand, and the spring means.
More particularly the aforementioned base portion of the rotation member has a lever, the mounting stand has the spring means and a spring receiver, the lever directly abuts the mounting stand to allow a rotation force of the base portion to be directly transmitted to the mounting stand when the base portion rotates in one direction, and the lever abuts on the mounting stand via the spring receiver to allow the rotation force of the base portion to be elastically transmitted to the mounting stand via the spring means when the base portion rotates in the reverse direction.